In recent years, along with the progress made in lithography techniques in the preparation of semiconductor devices or liquid crystal display devices, formation of ultrafine patterns has been increasingly required.
With this trend of formation of ultrafine patterns, the wavelengths of the exposure sources also have tended to become shorter. Specifically, as the exposure source, ultraviolet rays such as g-ray and i-ray have been conventionally used, but currently, distribution of a semiconductor device using the KrF excimer laser or the ArF excimer laser is started. Furthermore, an F2 excimer laser that has a shorter wavelength than the above-mentioned excimer lasers, an electron beam, an EUV (extreme ultraviolet) ray, an X-ray, or the like are under investigation.
As one of the pattern forming materials for forming a pattern with a fine dimension, there is known a chemically amplified resist having a base component having film formability, and an acid generator component that generates an acid upon light exposure. The chemically amplified resists can be classified into two types, that is, a negative type, in which alkali solubility is reduced upon light exposure, and a positive type, in which alkali solubility is enhanced upon light exposure.
Conventionally, as the base component of the chemically amplified resist, there have been used a polymer, including polyhydroxy styrene (PHS), or a PHS-based resin in which a part of the hydroxyl groups of the PHS have been protected with an acid-dissociable, dissolution-inhibiting groups, a copolymer derived from a (meth)acrylic acid ester, or a resin in which a part of the carboxylic groups of the copolymer have been protected with an acid-dissociable, dissolution-inhibiting groups.
However, when a pattern is formed by using the above pattern forming materials, there arises a problem of roughness occurrence on the top surface or side wall surface of the pattern. For example, the roughness on the side wall surface of the resist pattern, that is, line edge roughness (LER) causes distortions around the holes in the hole pattern, or irregularities in the line width in the line-and-space pattern, which may produce an adverse effect on the formation of a fine semiconductor device.
The problem of the roughness becomes more severe as the pattern dimension is lessened. However, the polymer which is generally used as a base has a molecular size as large as several nm (root mean square radius per one molecule). In the developing process for the formation of a pattern, the dissolution behavior of the resist in the developer is typically analyzed in terms of one molecule unit of the base component, and as a result, as long as the polymer is used as the base component, it is extremely difficult to further reduce the roughness.
Under these circumstances, there has been proposed a resist using a low-molecular-weight material as a base component in order to provide extremely low roughness. For example, Non-Patent Documents 1 and 2 each propose a low-molecular-weight material containing an alkali-soluble group such as a hydroxyl group, and a carboxylic group, in which a part or all of the groups have been protected with an acid-dissociable, dissolution-inhibiting groups.
[Non-Patent Document 1] T. Hirayama, D. Shiono, H. Hada, and J. Onodera: J. Photopolym. Sci. Technol. 17 (2004), p. 435
[Non-Patent Document 2] Jim-Back Kim, Hyo-Jin Yun, Young-Gil Kwon: Chemistry Letters (2002), p. 1064˜1065